The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to etch film on a substrate such as a semiconductor wafer. The substrate processing systems typically include a processing chamber, a gas distribution device and a substrate support. During processing, the substrate is arranged on the substrate support. Different gas mixtures may be introduced into the processing chamber and radio frequency (RF) plasma may be used to activate chemical reactions.
In some processes, tungsten (W) film needs to be etched with very high selectivity to a hard mask layer, interlayer dielectric (ILD) such as silicon dioxide (SiO2) or other film materials. For example only, a thin W film may need to be etched in cross point memory structures during processing. In other examples, W film is recessed after a chemical vapor deposition (CVD) W fill step in memory structures including alternating oxide nitride (ON) or oxide polysilicon (OP) layers (e.g. ONON/OPOP memory structures).
In still other processes, both W film and film in a barrier layer need to be selectively etched relative to other film materials. In some examples, the W film may have voids. Therefore, etching of the W film and the film in the barrier layer need to be performed selectively relative to other film materials and without etching through voids of the W film.
Referring now to FIGS. 1A to 3D, various examples of etching of W film are shown. In FIGS. 1A-1B, a substrate 10 includes a W layer 12 arranged on one or more underlying layers 14. One or more layers 16 may be arranged on the W layer 12. A hardmask layer 18 may be arranged on the one or more layers 16 or the W layer 12. FIG. 1A shows the substrate 10 before etching while FIG. 1B shows the substrate 10 after etching.
In FIGS. 2A-2B, a substrate 30 includes multiple layers 32 that may be arranged on one or more underlying layers 34. A W layer 36 is arranged on the multiple layers 32. FIG. 2A shows the substrate 30 before etching while FIG. 2B shows the substrate 30 after etching.
In FIGS. 3A-3D, a NAND device includes a stack of layers 50 including fins 52 that are typically made of oxide film and intervening W film layers 54. During processing, the W film layers 54 need to be etched inwardly relative to ends of the fins 52 as can be seen in FIG. 3B. In FIG. 3C, barrier layers 58 are typically formed on the fins 52 during processing. The W film layers 54 may have voids 64 as can be seen in FIG. 3C. Etching in the voids 64 should be avoided. The barrier layers 58 may be made of titanium (Ti) or titanium nitride (TiN). During etching, the W film 54 needs to be etched back relative to the fins 52 (as can be seen at 66). The barrier layers 58 adjacent to ends of the fins 52 also need to be etched. If the barrier layer 58 is only partially etched at ends of the fins 52, the barrier layers 58 may short two or more adjacent W film layers.
Etching W film is typically performed using fluorine and/or chlorine plasma gas chemistry at low pressure between 1 mTorr and 300 mTorr. In these processes, plasma damage tends to occur due to ions and radical flux generated during etching. As a result of the ion bombardment, mask selectivity is generally poor. The lateral recess is also difficult due to low radical density in these low pressure regime.